Method of drawing polyacrylonitrile containing fibres



United States Patent 3,449,485 METHOD OF DRAWING POLYACRYLONITRILE CONTAINING FIBRES Roberto Maria Costa and Franco Codignola, Milan, Italy, assignors to Societa Italiana Resine S.p.A., Milan, Italy No Drawing. Filed May 1, 1967, Ser. No. 634,874 Claims priority, application Italy, May 3, 1966, 10,083/ 66 Int. Cl. D01d 5/06; D01f 7/00 US. Cl. 264-182 5 Claims ABSTRACT OF THE DISCLOSURE The prior art processes generally use kerosene baths for both coagulating and drawing. In these processes, polymer is extruded into a coagulating bath maintained at rather high temperatures, mostly exceeding 100 C., the aromatic content being maintained at relatively low values on account of the high coagulating power of the aromatic compounds which makes the fibre spongy. The fibre is then drawn in a drawing bath, maintained at temperatures exceeding 100 C., and similarly of the kerosene type. This was necessary to effect as even a coagulation as possible and to aid in the the recovery of the solvent for the polymer. The coagulating bath, homogeneous at the operational temeprature, separated on cooling into two phases, the polymer solvent phase distilled to recover the solvent. The coagulating baths employed by these processes moreover exhibited a high concentration gradient with respect to the solvent for the polymer, so that the kerosene mixture flowing in a direction contrary to the filaments and actually deprived of solvent for the polymer on inlet, was enriched till it contained about 20% by weight on outlet, when it was fully regenerated by the abovementioned method.

It has now been found that filaments of excellent standard can be obtained, which have a very low absorption power for dirt, and are particularly lustrous, by extruding the solution of the polymer or copolymer of acrylonitrile into a bath kept at low temperature, said bath comprising cumene and the solvent for the polymer, thereupon drawing in a further bath, said bath comprising linear chain parafiins, having from l0-l6 carbon atoms in the molecule, the drawing bath kept at a temperature at least 30 C. higher than the temperature of the coagulating bath.

According to the preferred embodiment of the inven tion the spinning (coagulating) bath contains at any time a cumene percentage exceeding 50%, preferably 60% by weight.

The preferred acrylonitrile copolymers are those containing up to 20% of other monomers, such as metacrylonitrile, vinyl acetate and/ or acrylates, although polymers containing 100% polyacrylonitrile can be used.

The preferred solvent in the polymer solution is dimethyl-formamide, though other non-aqueous solvents known in the art may be employed, provided that they are sufficiently miscible with cumene so that they can be used in accordance with the invention.

3,449,485 Patented June 10, 1969 The polymer concentrations in the spinning solution, having regard to the operational temperature and average molecular weight of the polymer (which may be between 40,000 and 300,000) are preferably between 15 and 30% by weight.

The solvent for the polymer in the coagulating bath may have a concentration ranging between 15 and 35% by weight and may be adjusted depending upon the polymer concentration in the spinning solution and properties of the polymer, so as to be maintained Within very narrow limits, permissable variations amounting to few units percent.

This yields a product of constant properties over long periods under easily controllable running conditions.

Although parafiinic compounds may be altogether absent in the coagulating bath, according to the preferred embodiment these compounds are present in quantities up to 25% by weight. The temperatures of the coagulating bath preferably range between 30 and 70 C.

The process utilizes rather small coagulating baths such that the spacing of the inlet and filament outlet from the bath is shorter that 1 m. Moreover, the concentration gradient of the bath is low and the filament flows countercurrent to the coagulating solution.

The drawing bath comprising n-parafiins having 10 to 16 carbon atoms in the molecule is preferably kept at a temperature ranging between and 0, its length not exceeding 1 meter. During running, the conditions are adjusted so that the dimethylformamide concentration in the bath does not exceed 10% by weight, the cumene concentration is also kept below 10% by weight.

The use of this drawing bath avoids undesirable processes such as the formation of spongy products, when coupled with the above-described coagulating bath, more particularly when no paraflinic compounds are contained in the latter. In addition to the other advantages, this bath is easily regenerated.

Regeneration can be effected, for instance, by treating the solvent for the polymer with small quantities of water and by rectification of cumene, or, preferably, by rectification and consequent separation of the said two components and recycle thereof.

A peculiarity of the process is that threads of low titre (down to 0.2 denier) as well as threads of higher titre (up to 5 deniers) can be manufactured. Moreover, the filaments are well coagulated and capable of withstanding drawing ranging between 5 and 15 times the original length at a rate ranging between 50 and 200 m./min. (measured after drawing).

With the process threads can be obtained of a dry tensile strength ranging between 2.8 and 3.5 g./den. measured on an Uster dynamometer and of an elongation at break ranging between 25 and 35%.

Above all, the thread is of low dirt absorption, of particularly soft hand and highly lustrous. Finally, a product can be obtained which is lower than 1 in density, though the density range may extend between 0.95 and 1.10.

EXAMPLE 1 A 20% solution of acrylonitrile copolymer in dimethylformamide at 25 C. was prepared. The copolymer comprised 90.5 acrylonitrile and 9.5 methyl metacrylate and was of a molecular weight of 90,000 determined according to Staudinger. The resulting viscose was of a viscosity of 1.2 sec/cm. measured by steel balls 6 mm. in diameter at a temperature of 20 C.

The viscose was filtered and freed from air in vacuum at about 30 mm. Hg then extruded into a coagulating bath at 50 C. comprising 60% cumene, 20% dimethylformamide and 20% n-paraflins C C The n-parafiins were of the following properties: specific weight at 20 C.

r 3 0.7568, refraction index 20/20 C. 1.4258, the cumene being commercial cumene higher in titre than 99.5%.

The polymer solution was extruded at a linear rate of 4.6 m./min. into the coagulating bath through holes 0.10 mm. in diameter. The coagulating solution was fiowed countercurrent with respect to the filament which was collected at a rate of m./min. The replenishing rate of the bath was adjusted so that the dimethylformamide concentration at the outlet did not exceed 22 to 23% weight.

The thread was then drawn 10 times in a drawing bath containing the above described n-parafiins C -C at a temperature of 110 C. The length of the drawing bath was 1 meter. The fibre Was subsequently washed and dried at 120 C. by means of hot air. The drawing bath was adjusted to contain at any time not more than 5% by weight dimethylformamide.

A thread was obtained of 2.1 deniers of a dry tensile strength of 3.0 g./denier measured on an Uster dynamometer, having an elongation at break of 33%.

The product obtained upon washing and drying was particularly lustrous and of low dirt absorption. The density of the thread was measured at C. by suspending it in an aqueous salt solution at 20 C., exhibited values near one.

EXAMPLE 2 Under the conditions and with the apparatus described in Example 1, the solution of the copolymer described in Example 1 was extruded at a linear 2.2 m./rnin. into a coagulating bath comprising 70% cumene and 30% dimethylformamide by weight, kept at a temperature of 50 C. After drawing in the drawing bath at 100 C. under the conditions described in Example 1, washing and drying, a thread of 1 denier was obtained, of a dry tensile strength of 3.2 g./den., elongation at break 29%,

' its other properties comparing with those described in Example 1.

EXAMPLE 3 (Comparative) Under the conditions of Example 1 drawing was carried out in a boiling water bath. A spongy thread of low mechanical properties was obtained.

EXAMPLE 4 Under the conditions and with the apparatus described in Example 1, the solution of the copolymer described in the example was extruded at a linear rate of 1.1 m./min. into a coagulating bath comprising 70% cumene and 30% dimethylformamide, the bath kept at a temperature of 50 C. After drawing at 120 C., washing and drying a thread of 0.5 denier was obtained, said thread lustrous and of particularly soft hand, of a density of 0.98 measured in the above indicated manner, of dry tensile strength of 3.4 g./ denier and elongation at break of 27%.

What we claim is:

1. A method of preparing filaments from acrylonitrile polymers of acrylonitrile copolymers containing up to 20% by weight of other co-monomers selected from the group consisting of metacrylonitrile, vinyl acetate and vinyl acrylates, comprising the steps of (a) preparing a spinning solution containing 15 30% by weight of the acrylonitrile polymer or copolymer in .dimethylformamide solvent;

(b) extruding the spinning solution into a coagulating bath maintained at a temperature of about 30 C.- C., said comprising cumene in a quantity exceeding 50% by weight preferably exceeding 60% by weight, dimethylformamide in a quantity from 15%- 35% by weight and linear paraffins having 10 to 16 carbon atoms in the molecule in a quantity of 0%- 25% by weight;

(c) drawing the resulting filaments in a drawing bath comprising linear paraffins having 10 to 16 carbon atoms in the molecule maintained at a temperature exceeding by at least 30 C. the coagulating temperature, preferably 120 C.

2. A method of claim 1 in which the concentration of dimethylformamide in the coagulating bath is maintained within fairly restricted limits, permissible variations amounting to a few percent.

3. The method of claim 1 in which the drawing bath is maintained suchthat the polymer solvent concentration does not exceed 10% by weight.

4. The method of claim 1 in which the drawing bath is maintained such that the cumene concentration does not exceed 10% by weight.

5. The method of claim 1 in which the baths do not exceed one meter in length.

References Cited UNITED STATES PATENTS 2,967,085 1/1961 Sundea et al 26438 X 2,967,086 1/1961 Sundea et al. 26438 FOREIGN PATENTS 706,154 3/1954 Great Britain. 708,078 4/1954 Great Britain. 587,577 11/ 1959 Canada. 541,104 5/1957 Canada.

OTHER REFERENCES Condensed Chemical Dictionary, by Rose et a1., 6th ed., Reinhold, pp. 318, 319 and 777,1956.

JULIUS FROME, Primary Examiner.

J. H. WOO, Assistant Examiner.

US. Cl. X.R. 26438, 203, 210 

